A lifting device may hydraulically drive a hydraulic cylinder to lift and lower a lifting material. For example, patent document 1 describes such a known lifting device that is used for a forklift. A lifting device for a forklift lifts and lowers a fork (material handler), which serves as a lifting material, by supplying and discharging hydraulic oil to and from a hydraulic cylinder. This type of a lifting device includes a switch valve that controls the hydraulic oil flowing to a hydraulic pipe arranged between a hydraulic cylinder and the hydraulic pump. The fork is lifted, lowered, or stopped by controlling the opening and closing of the switch valve.
However, the switch valve may have different pressures at an inflow side and an outflow side of the hydraulic oil. Under this condition, if the lifting device for a forklift opens the switch valve to lower the fork, a shock would occur when the hydraulic oil starts flowing. Such a shock leads to unstable operation of the fork, which would move a carried cargo.
The lifting device of patent document 1 includes a means for solving the above problem. More specifically, the lifting device of patent document 1 temporarily activates the hydraulic pump to lift the fork when starting a lowering operation to decrease the pressure difference.